1. Field of the Invention
The present invention relates to an optical fiber which has a low transmission loss in a wavelength rang from 1300 to 1600 nanometers, an apparatus and a method for manufacturing the optical fiber.
2. Description of the Related Art
Reducing the transmission loss of optical fiber is enabled by a conventional technology in which, for example, a heating furnace which cools the optical fiber slowly is provided right under a drawing furnace, and the heating furnace cools the optical fiber at 500 to 1500° C. slowly to reduce the transmission loss of optical fiber (see Japanese patent Laid-open publication H04-59631). However, the transmission loss of optical fiber is not sometimes reduced even with the conventional technology. In this case, the transmission loss of optical fiber can be reduced by adjusting the viscosity of the core and the cladding (Japanese patent Laid-open publication 2002-148466).
However, it is not easy to control the species and the amount of dopant (Fluorine, Chlorine, and the like) for the core and the cladding and thereby to manage the viscosity or the refractive index of the core and the cladding. Accordingly, there are problems that a specific apparatus is required, thereby making the manufacturing apparatus for optical fiber complicated and larger, as well as increasing manufacturing steps and manufacturing time.